1. Technical Field
The present invention relates in general to joining dissimilar materials at a structural interface and, in particular, to an improved system, method, and apparatus for forming a compliant, non-corrosive interface between metallic and composite materials.
2. Description of the Related Art
Joining dissimilar materials such as metallic and composite components is a difficult and tedious process. There are many well known techniques for joining or forming joints between metallic materials. In the aerospace industries, composite components may be joined with prefabricated or preformed pi-shaped joints. For example, U.S. Pat. No. 6,718,713 to McKague describes a structural member having a planar base with two longitudinal legs extending in parallel from the base. A channel is defined between the legs for insertion of a flat plate that forms the first member of the structural member. The base of the preform is bonded to a composite member. The preform is a composite material having continuous filaments of woven or braided fiber. The preform is impregnated with a thermoset resin that bonds the first member to the second member of the structural member.
However, pi-shaped joints have not been used successfully to form metallic-to-composite joints because of thermal expansion mismatch and galvanic corrosion. Most metals have a significantly greater coefficient of thermal expansion than composite materials. Moreover, galvanic corrosion occurs when the following three conditions are met: (1) electrochemically dissimilar materials are used; (2) an electrically conductive path exists between the dissimilar materials; and (3) a conductive path exists for the ions to move from the more anodic material to the more cathodic material. One solution to these problems is described in the McKague patent referenced above. That patent uses filaments in the legs having a coefficient of expansion to match the plate, and filaments in the base having a coefficient of expansion to match the panel. Although that design is workable, an improved solution for forming a joint between metallic and composite materials would be desirable.